This is a renewal application, now in its 27'^ year. The purpose of this program is to train physician's who will be the future academic leaders in pediatric hematology/oncology. The program provides training at the postdoctoral level in the disciplines of protein chemistry, cell biology, molecular biology, developmental biology, immunology, neuroscience or genetics as they relate to the etiology and pathogenesis of blood disorders and cancer as well as translational/clinical research methodologies important in translating basic discoveries into humans. In this renewal application, new areas of training opportunities in translational research, immunodeficiency and stem cell biology have been outlined. The program primarily trains MD and MD/PhD candidates. It is expected that all MD candidates will receive training equal to a PhD and those who plan on a career in basic science research will receive additional training equivalent to a PhD postdoctoral experience. The training program is individualized for each trainee as they enter the program with different goals and experiences in research. We approach each trainee with the expectation that they will join the faculty of the division of hematology/oncology at Children's Hospital Boston (CHB) and Harvard Medical School as independent investigators following their training period. We have a special interest in training underrepresented minority candidates. Trainees are asked to begin investigating research projects and laboratories during the year before they begin their clinical fellowship. Training takes place in laboratories within the Boston area. The training program also offers significant didactic education. In addition, trainees are expected to attend seminar-style courses, formal lectures, and scientific conferences as well as participate in oral presentations. Training also includes assessment of trainees'ongoing research by trainee- specific scientific oversight committees. The "training faculty" who will participate in this grant includes subsets of CHB Hematology/Oncology faculty. Hematology faculty of the Brigham and Women's Hospital (BWH), the CHB Stem Cell Program, members of the Immune Disease Institute (IDI), in addition to faculty at other HMS institutions, and the Whitehead Institute and the Broad Institute at MIT. The training faculty have research funds totaling $36,165,934 per year representing 158 NIH grants. The program, seeking renewal for years 29-33 has trained more than 200 individuals and has a significant history of success in training leaders of American hematology and oncology throughout the academic hierarchy.